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Session 57 - Astrophysical Diagnostics from Polarimetry.
Display session, Wednesday, June 12
We present the results of a Monte Carlo radiation transfer investigation into the geometry of the circumstellar environments of Herbig Ae/Be stars. Our models calculate the emergent continuum flux and polarization arising from multiple scattering (off dust and electrons) and absorption (by dust and continuous hydrogen opacity) of stellar and envelope photons. We find that for a flattened circumstellar envelope, a polarization position angle flip of 90^\circ may exist between the optical and the UV. The flip occurs at the wavelength where the circumstellar envelope becomes optically thick in the equatorial regions so that stellar photons can only reach the observer by scattering into the line of sight from the optically thinner polar regions. This optical depth effect provides a wavelength dependence to the apparent scattering geometry and the wavelength at which the flip occurs is thus sensitive to the geometry and optical depth of the circumstellar environment. We apply our modeling scheme to the UV through near IR spectropolarimetric data on the Herbig Ae/Be stars HD45677 and HD163296 which both show 90^\circ position angle flips at different wavelengths in their spectra.
Program listing for Wednesday